imwritemulti is missing from the type stubs.

However, the corresponding imreadmulti is present.

Looks like this overloaded function was merged into OpenCV 4.5.1:

• Issue: imwrite: multi-image overload for bindings opencv/opencv#18533
• PR: imwrite: multi-image overload for bindings opencv/opencv#18533
• Main tree: Merge 4.x opencv/opencv#18951
• Release: https://github.com/opencv/opencv/releases/tag/4.5.1

The current cv2 type stubs are generated from 4.4.0. When will it be time to update to a newer version? OpenCV stable is at 4.7.0 already.